Manufacturers of aerosol cans and other pressurized dispensing containers are continually compelled to seek ways to achieve conflicting goals. One of those goals, for example, is the capability of obtaining high dispensing pressure in a can. The attainment of this goal, however, is frequently hindered by the fact that the means for achieving such pressure occupies some of the volume that would otherwise be reserved for the product. An example of this is the use of a piston which exerts upward force against the product in the can by means of compressed air beneath the piston. A simpler example of the dilemma, of course, is where compressed gas alone is used in the container after it has been sealed; the volume occupied by the compressed gas cannot otherwise be used for storing dispensible product.
Another goal of the art is to provide a pressurized container that achieves substantially complete expulsion of the product. The use of compressed gas for this purpose, however, is fraught with delays and additional expense incurred during manufacturing and packaging. Where high pressure is desired, sufficient space must be reserved within the product container for the propellant gas at an intended pressure. The product must usually be placed within an unsealed container, which is then sealed, and subsequently a propellant must be introduced, under pressure, into the can through the valve or plug. The gas charging stage requires considerable time. Where the compressed gas is dissolved into the product, the manufacture must suffer delay while the gas dissolves into the flowable or sprayable material. While carbon dioxide affords high pressure when used as a compressed gas propellant, the process of dissolving the carbon dioxide into the product is commercially undesirable because it takes several hours to accomplish.
Manufacturers have turned to methods employing carbon dioxide, in part, because of an increased awareness of the deleterious effect of chlorofluorocarbons on the stratospheric ozone layer and because of the attractiveness of placing the pressure generating system within the container. As disclosed in U.S. Pat. No. 3,718,236, a system is used for generating carbon dioxide gas by combining sodium bicarbonate and citric acid within a sealed bag-like structure that is free-floating within the dispensing container. In one disclosed embodiment, the inflatable bag includes a number of sealed compartments containing solid tablets of sodium bicarbonate. The sealed compartments are sequentially ruptured as product is expelled, permitting the sodium bicarbonate to combine with a mixture of citric acid and water also located within the inflatable bag, and gas pressure within the bag is thereby generated to expel the flowable product.
U.S. Pat. Nos. 4,373,341; 4,478,044; and 4,909,420 essentially follow the concept disclosed in U.S. Pat. No. 3,718,236 but introduce changes in the manner by which the inflatable bag and rupturable compartments are constructed or fabricated. The bag-like structures disclosed in those patents are relatively complex. They also require additional expense, materials, and manufacturing steps. Further, these structures involve the citric acid and sodium bicarbonate reaction only after the dispensing can is sealed, and they require that the reaction be initiated and that it occur throughout the dispensing life of the container. These structures are intended to maintain constant pressure, but do not provide an inexpensive and quick manner of charging the container with immediately active carbon dioxide which is stored for use upon demand within the contained product.
In view of the foregoing limitations and objectives, a method is needed for pressurizing a dispensing container in an economical, convenient, and expeditious manner.